Many conventional computing systems typically include voltage regulators to regulate voltage supply input to the computing systems. In general, the output voltage (Vout) of a voltage regulator is approximately Vout=Vin*Thi/Tperiod, where Vin is the input voltage to the voltage regulator, Thi is the period of time in which Vin is above a certain threshold (also referred to as being high), and Tperiod is the period of Vin. Thi/Tperiod is also commonly referred to as the duty cycle of Vin. Rather than directly working from the above equation, many voltage regulators use closed loop control to find the appropriate high time that yields the desired Vout.
When a computing system, such as a portable personal computer (a.k.a. a laptop computer), is connected to or disconnected from an alternating current (AC) power supply (a.k.a. wall power) while being powered on, the Vin transient produces a Vout transient, which the closed loop control has to correct. Prior to correction, there may be a Vout transient, which may potentially be high enough to damage circuits in the computing systems. Thus, to prevent potential damage to the computing systems, the Vout transient has to be guardbanded around. However, the increased guardband may in turn force a higher voltage, which may drain a portable power source of the computing system (e.g., a battery) more quickly.
A conventional solution to the above problem is to sense Vin and to adjust the duty cycle of Vin accordingly. Specifically, one conventional technique is to multiply Thi by the ratio (Vin—old/Vin—new), where Vin—old is the previous value of Vin and Vin—new is the current value of Vin. However, the ratio implies a division by Vin—new, which is a very costly digital logic function to implement in semiconductor circuits.